Free Radical Grafting of Epigallocatechin Gallate onto Carboxymethyl Chitosan: Preparation, Characterization, and Application on the Preservation of Grape Juice

Abstract

In this study, carboxymethyl chitosan (CMCS) was combined with epigallocatechin gallate (EGCG), a natural antioxidant polyphenol, by a free radical grafting procedure to enhance its application potential on the preservation of fruit juice. The successful formation of EGCG-grafted CMCS (EGCG-CMCS) was confirmed by ultraviolet–visible absorbance, Fourier transform infrared spectroscopy, and proton nuclear magnetic resonance. The optimal molar ratio of EGCG to CMCS monomer was 0.5:1, which led to a grafting ratio of 47.8 mg/g in EGCG-CMCS. The X-ray diffraction patterns and thermal behavior showed that EGCG-CMCS had a lower crystallinity and thermal stability than CMCS, which is probably due to the reduction in hydrogen bonds caused by grafting. Then, EGCG-CMCS was used as an additive for the preservation of grape juice. After storage at 4 °C for 7 days, the EGCG-CMCS–treated juice remained 90.6% of vitamin C, which was much higher than that of the CMCS-treated juice and the control. Similar results were also achieved for total phenolic content, total soluble solids, and titratable acidity. Moreover, EGCG-CMCS effectively maintained the antioxidant capacity and sensory color quality of the juice and inhibited microbial growth during storage. Our results suggest that ECGC-CMCS could be a promising biopreservative for fresh fruit juice.